Retroreflective structures of the type utilized herein are described in detail in Jungersen, U.S. Pat. No. 2,380,447, issued Jul. 31, 1945, Hoopman, U.S. Pat. No. 4,588,258, issued May 13, 1986, and Stamm, U.S. Pat. No. 3,712,706, issued Jan. 23, 1973 (each of which is incorporated herein in its entirety by reference.)
Walter, U.S. Pat. No. 5,171,624 discloses microprism reflective sheeting in which prism pairs are tilted with respect to one another at an angle of 3-10xc2x0, a prism size of 0.006-0.025 (space between apices) and wherein at least one prism side surface is arcuate.
Benson, U.S. Pat. No. 5,122,902 discloses retroreflective cube-corner elements with separation surfaces between elements and truncated cube-corner elements.
Conventional retroreflecting prism or corner cube arrays of the type described in U.S. Pat. No. 5,171,624 (incorporated herein by reference in its entirety) create a diffraction pattern having a characteristic void outside of a central maxima and a six lobed light energy distribution. The six lobes of energy formed about the central maxima represent the energy cones of the first order of diffraction. Such an energy distribution is undesirable because of the high degree of variation of energy level throughout the retroreflected beam.
The above-referenced patent, U.S. Pat. No. 5,565,151, discloses retroreflective prism sheeting comprising an array of closely spaced prisms in which a window is formed in at least one of the facets of a prism in a prism pair.
The windows are formed by casting the prisms in a mold in which a section of the prism element mold is removed.
Removing a section of one of the prism elements creates a smaller prism which produces increased observation angle performance. Good observation angle performance is especially important for retroreflecting objects viewed by trucks or airplanes where the source of light is spaced a further distance from the driver than an automobile. Such improved performance is also important for automobile drivers when the driver is very close to the retroreflecting object.
In accordance with the present invention, the prism facets and/or the windows as formed in a mold are textured so as to provide light scattering of the incident light in certain areas which greatly enhance the whiteness (CAP Y) of the retroreflective film. Enhanced whiteness increases the conspicuity of the film; a property highly desired in daytime and nighttime viewing of objects. The texturing is in the form of a random speckled pattern of sufficiently small texture as compared to the prism aperture to cause light retroreflected from the prism facets to be deviated or scattered slightly, resulting in a more uniform energy distribution of the retroreflected light and wider observation angle performance.
In accordance with another embodiment of the present invention, a prism tool or mold is provided having indentations or projections formed on the mold facets or windows for texturing the prisms, as made or formed in the mold.